US hopes of building a missile defence system in central Europe have been called into question by demands from Poland’s new centre-right government that has made its agreement to the plan contingent on Washington committing to improve Polish air defences.

“Our agreement for anti-missile installations in Poland will be directly linked to the prospect of increasing Poland’s security,” Donald Tusk, Poland’s prime minister, said earlier this week, adding that he was “responsible for the safety of Poles, and not the safety of the United States”.